Here's a press release from Keynote Systems that got 75 people to complete assorted web-based tasks on their iPhones -- a fairly typical usability set-up. One of the top bullet points in the press release: "advertising on the mobile web not compelling for users to click through." But if you look further down, one of the company's findings is that "only four percent of users tapped into advertising; nearly a quarter noticed advertising but did not click through."

What do they mean by "tapped"? A 4-percent click-through? How much of it can be attributed to mis-clicks?

An earlier press-release by the ad network AdMob: "Ads on the iPhone deliver strong engagement for advertisers with triple, on average, the already high click-through-rates seen on mobile."